Fig 5. Spectral editing for identification of functional groups in 3-month decomposing wheat straw under anaerobic (left) and aerobic (right) conditions: (a, b) nonselective cross polarization/total sideband suppression (CP/TOSS) spectra for reference, with a contact time of 1 ms at a spinning speed of 5 kHz; (c, d) corresponding dipolar dephasing CP/TOSS spectra showing nonprotonated carbons and mobile carbons, acquired after 40-μs of decoupling gated off; (e, f) selection of sp³-hybridized carbon signals by a ¹³C chemical shift anisotropy (CSA) filter with 35-μs filter time, other parameters as in (a); (g, h) corresponding selection of protonated sp³-hybridized C signals with a 35-μs CSA filter and short 50-μs CP; (i, j) selection of nonprotonated or mobile sp³-hybridized C signals with a 35-μs CSA filter and 40-μs dipolar dephasing; (k, l) selection of relatively immobile CH and CH₂ signals with small residual CH₃, which was achieved by finding the difference between a short-CP spectrum and a spectrum of short CP combined with dipolar dephasing.

All the spectra were normalized to the highest peak. Recycle delays for all the spectra were 1 s and the number of scans was 6144.